Apparatus for coating strip-form substrates

ABSTRACT

A machine for coating a layer of a viscous emulsion on a movable support having a feed means operatively associated with the support with a narrow gap between the feed means and the support for forming the viscous emulsion into a layer on the movable support. The feed means contains a chamber opening into the narrow gap, and the machine is arranged so that the viscous emulsion fed from the chamber and formed by the narrow gap is under an adjustable static differential in pressure between the inlet end of the narrow gap which has a lower pressure on the emulsion and the outlet end of the gap which has a higher pressure. A cavity in a wall-adjoining the chamber in the feed means has one opening into the chamber sidewall and containing a compressible gas acts as an air cushion and reduces the variations in pressure on the feed material during feeding as the gas is enclosable within the cavity by the passage of feed material through the chamber.

United States atent Herzhoif et al. 1 1 Feb. 1, 1972 [54] APPARATUS FORCOATING STRIP- 3,206,323 9/1965 Miller et al ..118/50 X FORM SUBSTRATESPrimary Examiner-John P. McIntosh [72] Inventors: Peter Herzhoff,Leverkusen; Hans Gref, c n and Hutz Cologne-Stammherm; Rolf Behr,Leverkusen; Fritz Maus, CologneFlittard; [57] ABSTRACT WolfgangSchweicher; Willi Wasser, both of Level-kusen; Josef Friedsam, A machinefor coating a layer of a viscous emulsion on a Langenfeld; KurtBmwatzki, opladenq movable support having a feed means operativelyassociated all Germany with the support with a narrow gap between thefeed means [73 1 Assignce. Agfa cevaert Akfiengeseuschafl Lave and thesupport for forming the viscous emulsion into a layer kusen, Germany onthe movable support. The feed means contains a chamber opening into thenarrow gap, and the machine is arranged so Filedl 1 that the viscousemulsion fed from the chamber and formed by the narrow gap is under anadjustable static differential in [211 Appl- 797809 pressure between theinlet end of the narrow gap which has a lower pressure on the emulsionand the outlet end of the gap [52] U.S. Cl ..118/50, 1 18/410 which hasa higher pressure. A cavity in a wall-adjoining the [51] Int. Cl. .rBOSc5/02 chamber in the feed means has one opening into the chamber [58]Field of Search .1 18/50, 410, 41 1,412, 50.1 sidewall and containing acompressible gas acts as an air cushion and reduces the variations inpressure on the feed [56] References Cited material during feeding asthe gas is enclosable within the cavity by the passage of feed materialthrough the chamber. UNITED STATES PATENTS 3,067,060 12/1962 Glaus ..1'18/324 x 2 Clams 1 Draw PATENTEDFEB HHTZ 3.538.604

INVENTOR I;:

APPARATUS FOR COATING STRIP-FORM SUBSTRATES This invention relates to aprocess for coating substrates in strip form with viscous solutions,preferably with photographic emulsions, in which the substrate is wettedin a sealed coating chamber whose end at the point where the emulsionemerges is formed by a coating gap several times wider than the wetfinished layer is thick, and in which to counteract the forward movementof the moved substrate, layer formation is effected under an adjustablestatic pressure differential between the inlet end and outlet end of thegap, the lower pressure prevailing at the inlet end.

It has been found in practice that static pressure differentialsequivalent to a water column of from 20 to 250 mm. are needed to formthe required thicknesses with conventional emulsions.

One disadvantage affecting the practical application of the process isthat an alternating pressure is superimposed upon the static pressuredifierential as a result of inevitable vibration in the coater,producing periodically alternating thick and thin zones, so-called crosscuts," in the emulsion layer leaving the coater. For example, vibrationsaffecting the coater at a frequency of 25 c./s. are inevitable despitecareful antivibration screening on account of the three-phase motorswhich rotate in the coating machine at a speed of approximately 1,500r.p.m., corresponding to 25 c./s. If this vibration has an amplitude ofonly 2;; for example, this gives rise to an alternating pressure ofapproximately 50 mm. of water, in other words a value which iscomparable to the static pressure differential governing layerthickness.

It has now been found that this alternating pressure emanating fromvibration can be reduced to a harmless extent by providing inside theemulsion chamber of the coating machine a cavity in which a cushion ofair is enclosed when the coating chamber is full. This cavityadvantageously extends over the entire width or almost over the entirewidth of the coating machine.

In this way, both the air and the emulsion volume behave like twoseries-arranged elastic media the softer of which, namely the air,eventually determines the amplitude of the alternating pressure created.At a given frequency and vibration amplitude, the amplitude of thisalternating pressure is proportional to the resistance of the medium ofsound waves. The resistance of air to sound wave is lower by a factor of3,600

than that of water, which means that the alternating pressure created isreduced by this factor. Accordingly, the residual-alternating pressureamplitude is three to four times smaller than the static pressuredifferential governing layer thickness at the coating gap, with theresult that it is no longer able to produce any noticeable cross cut inthe coating.

The apparatus according to the invention is diagrammatically illustratedby way of Example in the accompanying drawmg.

A roll 5 provides a rotatable support for the substrate to be coated asit passes the coating machine 4. A gap 6 is defined between thesubstrate supported by the roll 5 and the coating machine 4. A chamber 3at the inlet end of the machine provides a low pressure at the inlet endof the gap. The coating machine 4 is provided with an internal emulsionchamber 2 which is supplied with coating material as indicated by thearrow in the drawing. A cavity 1, in which a cushion of air is provided,is in communication with the chamber 2.

What we claim is:

1. In an apparatus for coating a layer of viscous material on a movablesubstrate which includes the combination of a movable substrate, asealed coating chamber for wetting the substrate, a viscous material forfeeding onto said movable substrate, a coating machine for depositingthe viscous material on the substrate containing the sealed coatingchamber and being operatively associated with the substrate having oneend associated with the substrate so as to form a narrow gap between thecoating machine and the substrate, the gap having an inlet end at whichthe substrate enters the gap and an outlet end at which the substratedeparts from the gap, and including means in the combination or applyinga static pressure differential at a lower pressure at the inlet end anda higher pressure at the outlet end of the narrow gap, and in which theviscous material is fed from the coating machine through an opening fromthe chamber into the narrow gap, the improvement consisting of a cavitylaterally adjoining the said chamber having an opening into the chamberthrough a chamber sidewall and containing a compressible gas, said gasbeing encloseable within said cavity by said conveyed viscous materialto maintain said static pressure differential and reduce variations inpressure on said feed material.

2. An apparatus as claimed in claim 4, wherein the cavity occupiessubstantially the entire width of the coating machine.

2. An apparatus as claimed in claim 4, wherein the cavity occupiessubstantially the entire width of the coating machine.